1. Field of the Invention
The present invention relates to a photosensitive body having a conductive substrate provided thereon with a photosensitive layer of an organic substance and more particularly to a photosensitive body which has an intermediate layer between a conductive substrate and a photosensitive layer and which can stably provide excellent images.
2. Description of the Prior Art
A photosensitive body for electrophotography used in the Carlson's electrophotography (hereinafter also referred to as simply "photosensitive body") has mainly included inorganic photoconductive materials such as selenium, selenium-tellurium alloy, selenium-arsenic alloy and zinc oxide. However, there have intensively been proceeded the development of photosensitive body having organic photoconductive material form the viewpoint of non-pollution properties and good film-forming ability and they have been put into practical use. Among these, there have been forwarded the development of so-called separated functional photosensitive body in which the photosensitive layer is separated into a charge-generating layer and a charge-transfer layer. This is because, it is highly probable that the separated functional photosensitive body can ensure a high sensitivity and a long lifetime through the combination of a charge-generating layer including a charge-generating substance having a high charge-generation efficiency and a charge-transfer layer including a charge-transfer substance having a high charge mobility.
Most of the separated functional photosensitive bodies which make use of organic photoconductive materials presently accepted have a structure which has a conductive substrate such as an aluminum substrate provided thereon with, in order, a charge-generating layer and a charge-transfer layer. As the thickness of the charge-generating layer increases, the charges generated within the charge-generating layer are not smoothly injected into the charge-transfer layer and the conductive substrate and this becomes a cause of various disadvantages such as formation of memories, a decrease of charging characteristics during repeated use and an increase in a residual potential. The thickness of the charge-generating layer must be as thin as possible and in general in the order of submicrons so as not to become such cause of the above disadvantages. To ensure sufficient absorption of incident light rays through such a thin film, the charge-generating substance must have a high absorptivity coefficient and a high charge-generating efficiency. Presently, pigment type substances have mainly been used as such charge-generating substances with satisfy the foregoing requirements.
Since a charge-generating layer is applied onto a conductive substrate in the form of a very thin film as has been described above, contaminants present on the surface of a substrate and non-uniformity of the shape thereof lead to the easy formation of uneven film. The formation of such an uneven film in turn leads to various image defects formed on photosensitive bodies such as missing of images, formation of black specs, uneven density of images and fogging. To solve these problems, many attempts have been directed to the development of, for instance, washing methods which can remove the contaminants present on the surface of substrates, materials for substrates which can inhibit the chipping phenomenon of the substrate during processing the surface thereof and improvement in finishing methods which allow the surface of the substrate uniform.
On the other hand, there has recently developed a laser printer which makes use of a laser as a light source for exposure and correspondingly attempts have been directed to the development of photosensitive bodies suitable for use in such a laser printer. In the laser printer, incident laser light rays for exposure (light for writing) reflected on the surface of a conductive substrate and the multiple reflection thereof within a photosensitive layer cause interference due to the coherency of the laser light and interference fringes due to this interference are appear on the photosensitive body as images, Japanese Patent Application Publication No. 60178/1990 discloses a method for solving this problem and which has roughening the surface of a substrate to inhibit interference of light rays. In this method, however, the surface of a substrate is intentionally made uneven and this results in the easy formation of an uneven charge-generating layer and accordingly the occurrence of image defects.
Moreover, Japanese Patent Application Publication No. 42498/1987 discloses a method for forming an intermediate layer between a conductive substrate and a photosensitive layer as methods for solving the problems of the formation of an uneven charge-generating layer due to contaminants present on the surface of the substrate and non-uniformity of the surface and as methods for forming an excellent uniform charge-generating layer on the surface of a conductive substrate whose surface is intentionally roughened to eliminate the formation of interference fringes. Examples of materials for such an intermediate layer include inorganic ones such as alumite and organic ones such as polyvinyl alcohol, polyamide, casein, gelatin and celluoise derivatives.
The foregoing intermediate layer must have a thickness sufficient for eliminating the influence of contaminants present on the surface of a substrate, non-uniformity of the shape thereof or the unevenness intentionally formed on the surface on the photosensitive layer subsequently applied to the surface thereof, while minimizing the deterioration of properties of the photosensitive layer due to the application of the intermediate layer. For this reason, the intermediate layer must have a low resistance sufficient for ensuring a current flow from the photosensitive layer to the conductive substrate. Moreover, it must inhibit the injection of charges from the substrate to the photosensitive layer after charging and, in other words, it must have blocking properties. However, the intermediate layers conventionally known do not always satisfy the foregoing requirements.